Field of the Invention
The present invention relates to rendering processing in a scan line image forming method.
Description of the Related Art
Conventionally, a method of forming an image of an object, such as an image, a graphic, and text, existing within a printing-target page in units of scan lines exists. In this scan line image forming method, in the case where a plurality of objects is included within a page, first, a closed area (span) demarcated by a contour of an object is detected. Then, from instructions to combine each object included in the detected span, image formation is performed after performing processing (hidden surface elimination processing) to eliminate an object unnecessary in drawing of each span. For example, Japanese Patent Laid-Open No. 2013-004032 has disclosed a technique to process a page on which objects, such as graphics, overlap at a high speed by deleting unnecessary overlap edges to reduce the number of objects.
A printing apparatus having received PDL data as printing instructions generates final print data by temporarily generating intermediate data (rendering processing). The maximum value of the memory capacity for storing this intermediate data is determined in advance. For example, in the case where the size of already-generated intermediate data exceeds the maximum value during generation of intermediate data of a certain page, the generation is temporarily stopped and an image (fallback image) in the bitmap format is generated from the already-generated intermediate data. Then, by deleting the already-generated intermediate, an empty area is produced in the memory, the data of the generated fallback image is compressed, and the image data after compression is stored in the memory in which an empty area is produced as intermediate data. Then, the generation of intermediate data of the page is resumed. This series of processing is called fallback processing.
In the case where the data of the fallback image generated and compressed by the fallback processing is decompressed later and then a bitmap image of the entire page is generated, conventionally, the decompressed image data is delivered by loading the image data onto a RAM area. However, access to the RAM area is performed via a bus, and therefore, the reading processing thereof requires much time. Consequently, it is considered to make use of a first-in-first-out memory (hereinafter, FIFO memory) that can be accessed without intervention of a bus in place of the RAM area to deliver decompressed image data. However, in the case where the FIFO memory is made use of for delivery of decompressed image data, it is not possible to appropriately read the decompressed image data of the fallback image in units of spans unless some processing is performed. Then, such a problem of defective reading of image data may occur similarly in the case of, for example, copy-forgery-inhibited pattern printing and form overlay printing.